The present invention relates to elevator systems and, more particularly, to elevator car position determining systems.
In the operation of elevator systems, it is desirable to stop an elevator smoothly and level with the landing for safety and comfort. In order to achieve a smooth, accurate stop the elevator system must initiate the elevator stop at the right moment in time. The leveling mode of operation and commencement of door opening must be timed properly. Most elevator doors begin opening a predetermined distance before the elevator car is actually level with the landing in order to speed up passenger transfer (the xe2x80x9cdoor zonesxe2x80x9d). To perform these functions for safe and accurate operation, it is necessary to monitor the exact vertical location of the elevator car at all times.
Prior art elevator car position determining systems typically utilize xe2x80x9ctape/sheavexe2x80x9d systems to monitor elevator car position. That is, a tape is connected directly to the elevator car and follows the elevator car""s vertical movement. The tape drives a sheave, which is typically located at the top of the elevator hoistway. The tape/sheave interface is a dedicated and positive traction mechanical connection. The sheave in turn drives a position encoder, i.e., a device to transfer positional data from one system of communication into another, which transmits precise positional data to an elevator controller once the system is properly calibrated. For example, high-rise elevator systems use either a digital encoder or primary position transducer (PPT) to provide elevator car position information to the elevator controller. The PPT is a digital encoder that is located in the machine room over the hoistway. Its rotatable component is driven by a steel-toothed tape that is attached to and runs with the elevator car when the car undergoes vertical movement.
To supplement positional information provided by the tape/sheave system, sets of steel bars or vanes are positioned throughout the hoistway so that position sensors mounted on the elevator car are actuated by the vanes (position sensor actuators) as the car moves vertically past. The vanes are typically mounted on the elevator guide rails or on a floating steel tape running the length of the hoistway.
The vanes located proximate to each elevator landing are called xe2x80x9clanding vanesxe2x80x9d and are used to mark approximate distances from the landing within which the elevator doors begin to open, necessitating coarse (outer door zone) and fine (inner door zone) adjustments to the elevator speed. Additionally, the landing vanes mark the approximate distance within which very fine adjustments are made to the elevator speed as the elevator car floor is leveled with the landing (the leveling zone). Typically, primary positional information is transmitted by the calibrated encoder of the tape/sheave system, while prior art landing vanes provide a rough check thereof.
xe2x80x9cAbsolute position vanesxe2x80x9d define physical and absolute positions in the hoistway, for the purpose of calibration upon installation or when the elevator car position is otherwise unknown, e.g., after a power failure where position information may be lost. Also, an xe2x80x9cup travel requiredxe2x80x9d vane is located in the bottom of the hoistway. The up travel required vane extends from just above the bottom distal end of the lowermost absolute position vane down to the extreme mechanical hard limit of the elevator car""s travel, i.e., full buffer compression. Detection of the up travel required vane indicates that the elevator car must be run in the xe2x80x9cupxe2x80x9d direction rather than the normal default direction of xe2x80x9cdownxe2x80x9d, when establishing an absolute position reference during a learning, i.e., calibration, run.
The system is initially calibrated upon installation, whereby a technician will put the elevator system through a semiautomatic xe2x80x9clearning runxe2x80x9d. During a learning run, the technician manually positions the elevator car at a specific initial position in the hoistway, e.g., at a point below the lowest absolute position vane. The technician will perform several runs from the initial position to determine, i.e., learn, the precise distances from the initial position to the transition edges of each vane. The position encoder will output a running pulse stream indicative of elevator car position relative to the initial position of the learn run. The precise position values corresponding to the transition edges of each landing are counted by a position counter and stored in a landing table as reference values. The reference values in the landing table are used to confirm elevator car position and are typically only adjusted when a new learn run is required.
However, xe2x80x9ctape/sheavexe2x80x9d systems, e.g., the Otis Elevonic 401 and 411 systems, are subject to wear and tape breakage, thereby disabling the elevator system until the tape is replaced. The replacement process is time consuming and expensive. In addition, such systems require additional and dedicated mechanical and/or electrical components that require installation, repair, maintenance and adjustment, all adding to the overall cost of the elevator system.
Because it is necessary for the position monitoring system to indicate the exact vertical location of the elevator car at all times, the prior art tape/sheave systems maintain a tape/sheave interface that has a positive traction, i.e., non-slip, mechanical connection. The precise position requirements make it difficult to substitute the dedicated tape/sheave components with other existing mechanical connections already present in the elevator system that are less prone to wear and breakage, but more prone to slippage. For example, the existing mechanical connection of the elevator""s safety system is a sheave mounted on a speed governor that is frictionally driven by a highly reliable wire rope connected to the elevator car. However, the accuracy of such a mechanical connection is less than ideal when used to determine the elevator car""s position, since it is heavily dependant on the frictional characteristics of the rope with the sheave. If such a connection were to be used, then as the wire rope slips over the sheave, the accuracy of the position data would be degraded. Therefore, compensating for this would be necessary since position cannot be guaranteed.
Moreover, prior art position determining systems, such as the tape/sheave systems, do not compensate for building settling phenomena. As a building settles over time, the location of a particular elevator landing relative to a specific calibration point in the elevator hoistway may change. Problematically, the landing vanes may also shift location independent of the changing locations of the landings, therefore significantly degrading the accuracy of the landing vanes"" positional information. This problem becomes more significant the higher the rise of the building. The settling phenomena in a tall building can require technicians to perform a new xe2x80x9clearning runxe2x80x9d as often as twice a year, thus incurring significant down time and expense to maintain the accuracy of the position determining system.
This invention offers advantages and alternatives over the prior art by providing a system of sensing elevator car position that dynamically compensates for problems due to frictional slippage of its mechanical connection between the elevator car and an encoder, and/or building settlement phenomena. Advantageously, the invention enables the position sensing system to be integrated into existing elevator systems, e.g., having an elevator speed governor system, in order to increase reliability and decrease cost. Moreover, by dynamically compensating for building settlement, the number of learning runs that have to be performed in the field are significantly reduced.
These and other advantages are accomplished in an exemplary embodiment of the invention by providing an elevator car position sensing system comprising an elevator car within an elevator hoistway of a building. An encoder is mounted within the elevator hoistway and mechanically connected to the elevator car, wherein the mechanical connection drives the encoder such that the encoder generates data indicative of the position of the elevator car within the hoistway. Either one of a position sensor and a position sensor actuator is mounted in fixed relation to a landing of the hoistway. The other one of the position sensor and position sensor actuator is mounted in fixed relation to the elevator car. The position sensor generates data indicative of the elevator car floor reaching a predetermined distance from the elevator landing when actuated by the position sensor actuator. An elevator position controller receives the data generated by both the position sensor and the encoder.
In an alternative embodiment of the invention, the mechanical connection comprises an elevator rope frictionally driving a governor sheave of an elevator speed governor system upon which the encoder is mounted. The elevator position controller utilizes data from the position sensor to dynamically compensate for degradation of positional data generated from the encoder due to frictional slippage of the rope.
In another alternative embodiment of the position sensing system, either one of the position sensor and the position sensor actuator mounted in fixed relation to the landing follows the changing location of the landing as the building settles. The elevator position controller utilizes data from the position sensor to dynamically compensate for degradation of positional data generated from the encoder due to the changing location of the landing as the building settles.
An alternative embodiment of the present invention utilizes an existing Emergency Terminal Speed Limiting Device (ETSLD), reference ANSI A17.1 of the Elevator Code, to substitute for dedicated absolute position vanes. The ETSLD is typically a set of positional vanes used in xe2x80x9creduced stroke bufferxe2x80x9d elevator systems to indicate speed and to keep the elevator car from going above a predetermined speed. By integrating the elevator car position tracking system with the ETSLD, mechanical component requirements and, thus, space requirements and maintenance costs are reduced.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.